1. Field of the Invention
Example embodiments generally relate to a fixing device, an image forming apparatus, and a method of dimensioning the fixing device, and more particularly, to a fixing device for fixing a toner image on a recording medium, and an image forming apparatus including the fixing device, and the method of dimensioning the fixing device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then collects residual toner not transferred and remaining on the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
Such fixing device may use a fixing film having a small heat capacity in place of the usual fixing roller to shorten the warm-up time of the fixing device. A heater provided inside a loop into which the endless fixing film is formed presses the fixing film against an adjacent pressing roller to form a fixing nip between the fixing film and the pressing roller through which the recording medium passes. As the recording medium bearing the toner image is passed through the fixing nip between the heater and the pressing roller by the fixing film, the fixing film heated by the heater and the pressing roller apply heat and pressure to the recording medium to fix the toner image on the recording medium.
However, the heater provided at the fixing nip has a drawback in that the fixing film heated by the heater increases the temperature of the recording medium as the recording medium moves through the fixing nip, resulting in a decreased gloss of the toner image fixed on the recording medium.
To address this problem, the fixing device may include a halogen lamp provided inside a hollow interior of a fixing roller not at the center of the fixing roller but offset to a position upstream from the fixing nip in the direction of rotation of the fixing roller. The pressing roller is pressed against the fixing roller to form a fixing nip between the pressing roller and the fixing roller through which the recording medium bearing the toner image passes. A temperature detector presses against the outer circumferential surface of the fixing roller at a position downstream from the fixing nip in the direction of rotation of the fixing roller to detect the temperature of the outer circumferential surface of the fixing roller. A temperature control circuit then controls power supply to the halogen lamp based on a detection signal provided by the temperature detector to adjust the temperature of the outer circumferential surface of the fixing roller at a predetermined temperature.
However, a drawback of the above-described arrangement is that, if relative positions of the temperature detector and the halogen lamp are not considered, the fixing roller may not be heated by the halogen lamp at the proper time. For example, a portion of the fixing roller which has a decreased temperature after heat is drawn by the recording medium at the fixing nip may already pass the halogen lamp when the halogen lamp starts supplying heat to the fixing roller. Accordingly, the portion of the fixing roller having the decreased temperature enters the fixing nip without being heated to a proper fixing temperature, resulting in faulty fixing of the toner image on the recording medium.